Protective films may be used to prevent filth such as dust from being attached to optical elements such as polarizing plates, other plastic products, home appliances, or automobiles, or to prevent occurrence of scratches. The protective films require proper peel strength and antistatic characteristics.
For example, when a protective film is rapidly peeled off for the purpose of use of products or assembly of other products, the protective film has to require relatively low peel strength (hereinafter referred to as “high-speed peel strength”). On the other hand, when the protective film is slowly peeled off, the protective film has to require relatively high peel strength (hereinafter referred to as “low-speed peel strength”) so as to exhibit a proper protective function.
Also, foreign substances such as dust may be generally absorbed by static electricity occurring during peeling of the protective film, or devices may be electrostatically damaged or malfunctions may be triggered in electronic products. In particular, the problems regarding the static electricity are being increasingly issued with the propagation of computers, and the integration of parts by multifunctionalization of liquid crystal TVs or mobile phones.
Therefore, many attempts have been conducted to give an antistatic function to a pressure-sensitive adhesive included in the protective film.
For example, Patent Document 1 discloses that an ethylene oxide-modified dioctyl phthalate plasticizer is blended with a pressure-sensitive adhesive to suppress the occurrence of static electricity. Also, Patent Document 2 discloses that an organic salt is added to a pressure-sensitive adhesive, and Patent Document 3 discloses that a metal salt and a chelating agent are mixed with a pressure-sensitive adhesive. However, the methods have problems in that contamination may occur by the transfer of pressure-sensitive adhesive components to products protected by the protective film, it may be difficult to prevent static electricity from occurring at the beginning, and, especially, the low-speed peel strength important for the protective function may be extremely low.